This study will examine the effect of pegvisomant on growth hormone excess in patients with McCune-Albright syndrome (MAS). Patients with this disease have polyostotic fibrous dysplasia-a condition in which areas of normal bone are replaced with fibrous growth similar to scar tissue, abnormal skin pigmentation (birth marks) and precocious (early) puberty. About 10 percent of patients have excess growth hormone (GH). GH stimulates the production of another hormone called insulin-like growth factor 1 (IGF-1). Together, GH and IGF-1 affect bone growth. The excess of these hormones in MAS can cause overgrowth of the bones of the face, hands and feet, excess sweating, or increased height.